1. Field of the Invention
This invention relates to an inspection device and an inspection method of a dielectric film, which is suitable for inspecting characteristic of a ferroelectric film of a ferroelectric random access memory or the like, and a method of manufacturing a semiconductor device.
2. Description of the Related Art
Volatile memories such as dynamic random access memory (DRAM), static random access memory (SRAM) and the like are used as a main memory of computers. The volatile memories retain data only when power supply is supplied. These data disappear when power supply is cut off. In contrast, a ferroelectric random access memory (hereinafter referred to as FeRAM) using a ferroelectric film has recently attracted a great deal of attention as a rewritable nonvolatile memory which does not lose data in case of cut off of power supply. The strength of a FeRAM is not only a nonvolatile memory but also low electrical power consumption and high-density design.
A conventional FeRAM comprises a ferroelectric capacitor 15 (hereinafter referred to as FeCap) which is shown in FIG. 8 and which is composed of a ferroelectric film 13 between two electrodes 12 and 14. The FeCap 15 is formed above e.g., a semiconductor substrate 11 with an insulation film (not shown) between them. This FeCap 15 is a functional main part of FeRAM; furthermore, it is often used as a sensor. The ferroelectric film 13 is composed of Perovskite materials such as Pb (Zr, Ti) O3 (hereinafter referred to as PZT) and the like. Both electrodes 12 and 14, which sandwich the ferroelectric film 13 in are often called an upper electrode and a lower electrode, respectively. Materials such as Pt, Ir or IrOx and the like are used for these electrodes.
Characteristic of FeCap must be stabilized for improving storage density of these FeRAM. Characteristic of Fecap tends to deteriorate when a ferroelectric film absorbs H2 or water vapor during manufacturing process of FeRAM. For example, H2 or water vapor tend to be produced during deposition process of an interlayer insulation film or an interlayer metal film. A capacitor with high resistance against dissociation of hydrogen is likely to possess higher reliability. Such characteristic deterioration tends to be facilitated when H2 is dissociated by a catalyst of metals such as Pt or Ir or the like which are used as materials of electrodes (S. Aggarwal, S. R. Perusse, C. W. Tipton, R. Ramesh, H. D. Drew, T. Venkatesan, D. B. Romero, V. B. Podobedov and A. Weber: Appl. Phys. Lett. 73 1973 (1998)). This dissociation represents a following chemical formula 1. “M” in the chemical formula 1 means a catalyst metal, and “−” in the right part of the formula means catalysis reaction.M+H2(g)→M−H2→M+2H+(g)M+H2O(g)→M−H+HO→M+H+OH  [Chemical Formula 1]
H2 is widely used during manufacturing process of FeRAM and produced as a by-product. In the case that reduced IrOx or Ir is used as a material of an upper electrode, H2 is dissociated into protons when it reaches to high temperature during manufacturing process. Furthermore, it will be diffused into a ferroelectric film such as a PZT film. As a result, ferroelectric characteristic will be deteriorated (K. Kushida-Abdelghafar, M. Hiratani and Y. Fujisaki: J. Appl. Phys. 85 1069 (1999) and J. S. Cross et al, Jap. J. Appl. Phys., 41 698 (2002)). Both rate of reaction and diffusion velocity are raised when H2 reaches to high temperature.
Recently, an experiment relating to deterioration of characteristics of a capacitor has conducted in reduction gas atmosphere which contains H2 or D2 under a high temperature situation. In this experiment, first, a capacitor is heated (baking) for a specific amount of time in a vacuum chamber which contains the above-described reduction gas atmosphere. Then, the sample is taken out of there, and an amount of remaining ferroelectric characteristic of the sample is measured in the air. By repeating this kind of heating up and measurement, time to disappear ferroelectric characteristic is calculated. This time is helpful information about process of a semiconductor device comprising FeCap when assessing resistance against dissociation of hydrogen of FeCap.
A problem of the above-described inspection method of a ferroelectric film is that it takes extremely long time because both baking in the chamber and measuring characteristic out of the chamber must be alternatively repeated many times due to uncalculated time to deteriorate ferroelectric characteristic. Furthermore, it is extremely difficult to identify actual time to deteriorate ferroelectric characteristic. This is because both the heat up process and the measurement process must be repeated many times until ferroelectric characteristic completely disappears.
FeCap is sensitive to water vapor, and hydrogen-induced degradation is observed during measurement of electric property (Chen et al. Appl. Phys. Lett., 80, 3587 (2002)). The following chemical formula 2 represents emergence of hydrogen.M+H2O(g)+e−→M−OH−Habs  [Chemical Formula 2]
This kind of reaction can be observed when an electric field is impressed on a capacitor in a specific measurement as the same reaction of hydrolysis.